The present invention relates to a plant cultivating apparatus. More particularly, the present invention relates to a plant cultivating apparatus in which cultivating conditions are artificially controlled.
As is well known, the growth of plants depends greatly on the environment. However, the natural environment on the earth varies and it is not always suitable for the growth of plants. The season when the natural environment has conditions suitable for the growth of plants is not present in some areas or is very short in other areas. Accordingly, conventionally, cultivation has been performed in facilities for artificially controlling environmental factors causing reduction of the productivity of plants to engender plant productivity at a level as high as possible. In these cultivation facilities, however, influences of the natural environment are not completely eliminated and, therefore, increase of plant productivity is limited.
Accordingly, attempts have been made to foster maximum plant growth in an artificial environment. Namely, plant factories have been constructed. In a plant factory, a plant is cultivated in an environment which can be optionally controlled, and completely controlled cultivation is possible. Accordingly, such a plant factory has many merits. However, in the above-described plant factory, since the environment is artificially prepared, the cost is increased because of consumption of energy. Accordingly, in order to make such artificial cultivation practical while utilizing the merits of such a plant factory, it is necessary to produce an energy saving effect and increase the productivity of the land used. Moreover, it is important to provide high-grade plants which are uniform in quality.
Plant cultivation in such a plant factory is carried out under artificial illumination in a building in which such conditions as temperature, humidity, carbon dioxide gas concentration and air speed are controlled. The property required for a light source suitable for this artificial illumination is that light having the necessary wavelength for the growth of plants be emitted at a predetermined intensity at high efficiency. The predetermined intensity referred to herein differs according to the kinds of plants that are to be grown. If this intensity is expressed in terms of illuminance, about 20 Klx is necessary for a weak-light plant and it is difficult to satisfy this requirement by using a single light source. Light sources having high luminous intensity and efficiency, such as high-pressure sodium lamps, mercury lamps, or metal halide lamps are used as the main light source in combination with fluorescent lamps to cover the wavelength.
When employing a central light source such as a high-pressure sodium lamp, the lamp should be disposed at a considerably higher position then the fluorescent lamps because the luminous intensity of one sodium lamp is very high. Otherwise, the plants cannot be irradiated at a uniform illuminance.
For example, in the case of lettuce, when cultivation is carried out at an illuminance of 18 to 20 Klx, if other environmental conditions are suitable, weight is increased 10 times in 7 to 8 days, and high-speed cultivation is possible.
As a means for reducing the power required for this artificial illumination, a method has been proposed in which a plant is irradiated at a low illuminance of about 5 Klx uniformly from all directions. According to this method, in the case of lettuce, the illumination power necessary for production of 100 g is only 0.65 KWH if an extremely high-efficiency fluorescent lamp is used. In a plant cultivated in such a way, the water content is about 95%, and the contents if inorganic substances (mineral) and vitamin C are as high as 30 mg/100 g. However, the method is defective in that the leaf shape of the plant is excessively long.
In the case where plants are cultivated with predetermined spaces provided between adjacent plants in a conventional plant factory as described above, even areas not requiring irradiation are illuminated, and therefore, an excess number of illuminating devices must be provided, requiring more equipment, land and building space. Accordingly, land utilization efficiency is low, and the cost of air-conditioning and other equipment and maintenance costs thereof are increased, having a great effect on production costs.
A means for obviating this disadvantage is provided in Japanese Patent Application Laid-Open Specification No. 55-24000. There a plant cultivating apparatus in which a plurality of pallets having plants placed therein are arranged in rows and a plurality of sets of pallets are arranged in a direction orthogonal to said rows. The space between adjacent pallets is increased in accordance with plant growth and the pallets are moved in a direction orthogonal to the row direction and fed to a harvesting line.
In such a plant cultivating apparatus, the speed of the movement of the pallets in the advance direction is changed in accordance with the growth of the plants to increase the space between the plants in the direction orthogonal to the row direction to provide an optimum space, whereby the amount of effective irradiation light is minimized by effective irradiation and the area occupied by cultivating facilities can be reduced.
In a conventional plant factory, because of the above-mentioned structure, since the luminous intensity per lamp is high when high-pressure sodium lamps or the like are used as the main light source, the lamps should be separated from the plants. Otherwise, the plant is not uniformly irradiated with light and the leaf temperature of the plant is excessively elevated injuring growth.
However, if the distance between the plants and the lamps is increased, the capacity of the building has to be increased, resulting in an increase in construction costs. Moreover, since the light should be dispersed, the efficiency of utilization of the light is inevitably reduced. Further, the quantity of air circulated in the building is increased and, consequently, air-conditioning costs are increased. On the other hand, in the case where a fluorescent lamp having good wavelength characteristics is used, since the fluorescence intensity is low, in order to obtain an illuminance of about 20 Klx, it is necessary to arrange many fluorescent lamps together without any substantial space between adjacent lamps.
Even at a low illuminance below 20, Klx, for example, at an illuminance of about 5 Klx, if plants are uniformly irradiated and cultivation conditions, such as carbon dioxide gas concentration and temperature, are maintained at appropriate levels, the plants can be grown at a high speed. Accordingly, in order to solve the above-mentioned problem in the use of fluorescent lamps, there may by be adopted a method in which the inner surface of a growing chamber is constructed with a reflecting plate having high light reflectance and the distance between the fluorescent lamp and the plant is shortened, whereby light of low illuminance is applied by using a small number of fluorescent lamps. In this method, however, if plants are cultivated close together so as to reduce the cultivated area and enhance land utilization, growth speed is reduced at such low illuminance as 5 Klx, and when the size of the plant leaves increases adjacent plants overlap each other. Consequently, the method is defective in that uniformly high-quality plants cannot be obtained.
As is apparent from the foregoing description, a low-illuminance, omni-directional irradiation plant cultivating system is promising as a power-saving technique, but in the cultivation of plants, where commercial value is influenced by the leaf shape, such as with lettuce, this system is not preferred from the view point of the product price because leaves grow excessively thus degrading the commercial value. Furthermore, if plants grow too long, the area occupied by plants in the plant cultivating bed is increased and, therefore, the equipment and illumination power costs are increased and cultivation becomes economically disadvantageous.
The above-mentioned conventional plant cultivating apparatus is constructed so that plants are supported by plate-like plant supports. However, as the plant grows, adjacent plants become too close to each other and the plant supports are covered with leaves of plants, while the plants grow leaning on plant supports. Accordingly, with an increase of the cultivation area, leaf portions of the plants fall down and the shape becomes bad. If the plants are uniformly irradiated with light, high-speed cultivation is possible even at a low illuminance. However, if the plants grow while leaning on the surface of the plant supports, reflection of light of the fluorescent lamp on the surface of the plant support is attenuated as the plants grow, with the results that uniform irradiation becomes impossible and reduction of the efficiency in photosynthesis of the plants is caused.
As pointed out hereinbefore, in the conventional plant cultivating apparatus, spaces between plants are increased only in a direction orthogonal to the row direction; but in the row direction, spaces corresponding to the size of fully grown plants are provided and these spaces are maintained throughout the cultivation period from the small seedlings stage to the mature plant stage. Accordingly, in the small seedlings stage the spaces are superfluous and the apparatus is defective in that effective utilization of the emitted light and floor surface cannot be attained.
As a means for overcoming this disadvantage, to broaden the spaces between pallets having plants placed therein in the row direction, troughs for guiding the pallets are radially formed and the respective pallets in the row direction are pushed out in the advance direction by a push-out rod. The push-out rod should cover the entire width when the spaces between the plants in the row direction become largest in the last stages where the plants are most mature. Accordingly, in the stages where the plants have not grown, the push-out rod is unnecessary. However, the length of the push-out rod cannot be reduced. Therefore, the total range covered by the push-out rod corresponds to the surface occupied by the plant cultivating apparatus and the method is defective in that the efficiency of utilization of the area of the land is very low. Consequently, this method is not suitable for practical application.
In conventional pallets having the above-mentioned structure, thinning operations have to be manually performed according to the growth of plants, and such pallets have unnecessary parts which contact the floor surface, increasing friction, with the result that excessive force is necessary for the moving device.
If the environmental conditions including light, are appropriately controlled, plants grow at high speeds with good reproducibility. A great deal of the problems involved in conventional plant cultivation techniques are economic problems, and, at present, the cost of the electric power for the light source for irradiating plants with artificial light is about 40% of the total manufacturing cost. In view of the manufacturing cost, this light source power cost is a heavy burden.